Foreword
In recent years, multi-functional applications such as adding cameras, GPS, mobile TV broadcasting, and NFC to mobile phones have attracted attention. At the same time, with the rise of high-end devices equipped with high-performance application processors such as smartphones and tablet devices, in addition to today's call features, it also adds comfort, fast browser, streaming media, data access, cloud-ready functions, not only It is a brand new service for navigation, and high-quality communication functions have become an essential element.
As a function jointly sought by these mobile terminals, we will exemplify the correspondence of various networks. The mainstream of mobile communication specifications to date is still a 2G system called GSM (Global System for Mobile Communications). The 3G system UMTS (Universal Mobile Telecommunications System), which is equipped with higher quality and faster data transmission than GSM, is now common. Recently, some major countries have begun services for this next-generation communication specification called LTE (Long-Term Revolution), and wireless can also perform high-speed data communication like wired.
A typical portable terminal usually cannot communicate data during a voice call. SVLTE (Synchronous Voice and LTE) communication services that can also perform data communication when voice calls are prevalent in North America. In addition, in China, through GSM for voice services, through TD-LTE (TDD system LTE) for data communication, the simultaneous SGLTE (synchronous GSM and LTE) communication services are also planned, IC manufacturers and The correspondence of the assembly manufacturers has also been carried out quickly.
TDD and TD-LTE
The TDD (Time Division Duplex) refers to a method in which radio waves of the same frequency are used for the uplink and downlink lines by one of the communication methods of the base station and the mobile terminal in both directions. In contrast, the way in which the upstream and downstream lines use different frequency waves is called FDD (Frequency Division Duplex).
Figure 1: Comparison of TDD and FDD
LTE is the communication specification for mobile phones. This specification was certified by the standard 3GPP organization (3rd Generation Partnership Project) in March 2009. It is an intermediate technology between UMTS (3rd generation mobile phone) and the future 4G (4th generation mobile phone). At that time, it was called 3.9G. It was renamed 4G because it was approved by the ITU (International Telecommunication Union). Name it like this.
In general, in most cases, FDD-LTE using FDD is called LTE, not FDD-LTE, which is distinguished from LTE-like TD-LTE using TDD. TD-LTE can transmit and receive at the same frequency. It can be said that the frequency configuration is relatively simpler than FDD-LTE. TD-LTE basically has the same technical difference as FDD-LTE except for the difference between FDD and TDD. It uses the same frequency band as 3G, and can be bandwidth width 1.4, 3, 5, 10 according to different situations. 15, 20MHz choose to use. LTE only supports packet communication. Voice communication is supported by VoIP technology called VoLTE. Generally speaking, it mainly supports data communication. It takes time to truly popularize voice services. TD-LTE is a service project that China is actively promoting. Japan has also begun to use 2.5GHz bandwidth for services. North America is also planning, and it is obvious that it will become popular all over the world.
TD-LTE RF circuit
As shown in FIG. 2, it is a circuit diagram of TD-LTE (SGLTE).
Figure 2: Circuit diagram of TD-LTE (SGLTE corresponding)
In the current TD-LTE corresponding terminal, in order to correspond to voice calls, triple mode and dual mode GSM and UMTS are indispensable. GSM has foreseen the problem of overseas roaming. Therefore, it can generally correspond to four different frequency bands of 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz, and each of the frequency bands on the receiving side is equipped with filters one by one. The band1 of UMTS is FDD, so a duplexer (antenna duplexer) is required.
In China, the frequency band for TD-LTE is classified into Band38, Band39, and Band40 according to 3GPP. Since it is a TDD system and does not require a duplexer, the transmission side has a filter corresponding to high power, and two credit filters are used on the main circuit side. The LTE system corresponds to the MIMO technology, and since it is a multi-antenna structure, a plurality of circuit sides are equipped with a credit filter.
Take a deep breath, close your eyes, the world has the freshest oxygen ... Yu Quan's "Deep Breath" is well known to us, but as the environmental problems become more and more serious, the haze sky also increases, PM2.5 PM10 and so on Vocabulary has also been mentioned more and more, and air purifiers have quickly become popular on the market with this "air quality" trend. Along with this, the air-clean brand has sprung up, and various technologies are dazzling. Which ones are indeed effective and which are just tasteless propaganda? How does the Air Purifier bother us to get rid of pollution? And look at the editors for you.
Analysis of air purifier
The critical value of PM2.5 content is 75 μg / m3
The pollutants in the air mainly include soot, total suspended particulates, inhalable particulates (PM2.5) and fine particulates (PM10). The smaller the diameter of the particulates, the deeper the part that can enter the respiratory tract. 10 micron diameter particles It is deposited in the upper respiratory tract, and particles below 2 microns can penetrate 100% into the bronchiole and alveoli.
1k-5k air purifier prices vary greatly
The air purifier products on the market not only have various functions, but also have prices ranging from thousand yuan to tens of thousands. The pricing of imported products is generally higher than that of domestic brands. Except for the core technology of many brands, the promotion of purification effects is similar, and consumers need to choose according to demand.
The air quality standard of 74 key cities is only 4.1%
According to the data of the press conference held by the State Council Information Office on June 4, according to the new "Ambient Air Quality Standards", the six pollutants SO2, NO2, PM10, PM2.5, CO and O3 were evaluated, 74 new standards In the first phase of monitoring and implementation, the proportion of cities that met the ambient air quality standards was only 4.1%, and the other 256 cities implemented the old air quality standards, and the proportion of cities that met the standards was 69.5%.
Air purifier sales increased by 90.5% compared with last year
According to a report recently released by the China Electronics and Information Industry Development Institute, due to the haze weather, air purifiers have become the most concerned home appliance products, with sales of nearly 2.4 million units nationwide last year, a year-on-year increase of 90.5%; retail The amount reached 5.6 billion yuan, a year-on-year increase of 105.9%.
HEPA filter needs to be replaced in March
The filter of the air purifier Air Cleaner is the same as the filter of the water purifier, and it is not effective for a long time. After long-term use, the accumulation of dust on the surface of the filter will also cause the filter to gradually fail. Therefore, when the haze is more serious, the non-washable HEPA filter needs to be replaced every three months.
Merchants claim that the purification rate is more than 99% for the concept of stealing
99% or even 99.99% seems to have become a slogan for many air purifiers on the market. Many brands of products promote their high removal rate of PM2.5 and formaldehyde. In fact, this kind of publicity is more of a kind. The slogan of stealing the concept, the removal rate of 99% is the effect of the material itself on PM2.5 and formaldehyde, not the effect of actually running in space.
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